Apparatus for drawing sheet metal blanks



July 31, 1956 A, RS

APPARATUS FOR DRAWING SHEET'METAL BLANKS Filed April 24. les

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ANTHONY PETERS y 31, 1956 A. PETERS 2,756,707

APPARATUS FOR DRAWING SHEET METAL BLANKS Filed April 24. 1952 3 Sheets-Sheet 3 FIG. 5

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m2 ANTHONY PETERS ATTORNEY United States Patent APPARATUS non DRAWING SHEET METAL BLANKS Anthony Peters, New York, N. Y., assignor, by mesne assignments, to Baldwin-Lima-Hamilton Corporation, Philadelphia, Pa., a corporation of Pennsylvania Application April 24, 1952, Serial No. 284,013

7 Claims. (Cl. 113-44) This invention relates to a method and apparatus for drawing sheet metal blanks to any desired shape or form. More particularly, the invention relates to the type of drawing process wherein a pad of rubber, or similar flexible substance which acts like a fluid under pressure, is employed as the female die and a rigid punch is utilized as the male die, with means for supporting the blank, and relative movement between the punch and blank supporting means. Heretofore, the metal blank was supported on a pressure plate which confined the female die section, so that high pressure existed on one side of the pressure plate and blank and relatively low pressure on the other side. This was disadvantageous in those cases where, by reason of the shape into which the blank was to be drawn, a relatively large gap existed initially between the punch and the opening in the pressure plate in which the punch operated. It frequently caused the blank to be forced into the pressure plate opening, resulting in rupture of the blank. It is therefore an object of this invention to provide an apparatus wherein such substantial differential pressure does not exist on the blank, thus making it possible to draw shapes initially which heretofore could not be drawn. The elimination of such substantial differential pressure on opposite sides of the blank and pressure plate also makes it possible to employ a much thinner pressure plate than has heretofore been the case.

In drawing apparatus of the type mentioned above, it has been necessary to effect relative motion between the blank supporting means and the punch. These forces have been unit area multiplied by the area of the punch head or blank supporting means, whichever was movable. Such total forces frequently ranged as high as several thousand tons and required the application of extremely high external forces on the rear of the punch or blank supporting means to effect the blank forming operation. It is therefore another object of this invention to provide a method and apparatus whereby relatively small external forces will be suflicient to effect the forming operanon.

As described above, in blank forming apparatus heretofore employed the high forces developed in the forming operation were transmitted to the frame-work of the machine which had to be made extremely heavy to withstand loads on the order of several thousand tons. It is a further object of this invention to provide an apparatus wherein the loads transmitted to the supporting framework are greatly reduced, thus permitting the use of a relatively light-weight support for the apparatus.

Further objects and advantages of this invention will become apparent in the following detailed description thereof.

' In the accompanying drawings,

Fig. l is a vertical section through an apparatus embodying one form of this invention.

Fig. 2 is a view similar to a portion of Fig. 1, showing a modified form thereof.

Fig. 3 is a view similar to Fig. 2, showing another modification.

Figs. 4A and 4B are diagrammatic views illustrating the advantage of this invention in the drawing of a special type of form.

Figs. 5 and 6 are views similar to Figs. 2 and 3, showing still further modifications of the invention.

Referring to Fig. l, the invention is shown in the form of a casing comprising a pair of hollow rigid sections 10 and 11 which meet near their outer periphery on a surface 12, and are releasably locked together by a circular band 15 which hooks over the upper surface 16 of section 10 and has bayonet lock engagement 17 with section 11. A pressure plate 20 is supported adjacent its periphery between sections 10 and 11 so as to leave a substantial area unsupported by the casing sections. In this area there is an opening 21 within which the punch 22 operates. By reason of the relatively large unsupported area of pressure plate 20 it will be seen that there may be employed pressure plates having various sized openings 21 to accommodate different sizes of punch. Therefore it is only necessary to replace the pressure plate and punch to adapt the machine to drawing forms of various sizes. The pressure plate is designed to support thereon the blank 25 which is to be drawn over the head of the punch 22 as the punch and plate are moved relative to each other, the punch passing through opening 21. The section 10 is filled with a flexible member of a material which acts like a fluid under pressure, This material may be a flexible shape-forming substance, such as rubber, and be provided with an annular expansible chamber 30 adapted to be filled with fluid so that any desired pressure per unit area may be developed. Such pressure may be supplied from any suitable source of hydraulic pressure 32 and enters the casing section 10 by conduit 33 and inlet tube 34. The casing may be supported by a frame F to which casing section 11 is fastened by bolts 35 and casing section 10 by bracket 36 and bolts 37, 38. The bolt 38 is fixed to the upper end of a piston 26 operating in a hydraulic cylinder 27. When the lock member 15 is turned to unlock casing sections 10 and 11, hydraulic pressure may be delivered to cylinder 27 to lift casing section 10 to permit withdrawal of the formed blank and the insertion of a new blank.

By locking the two sections 10 and 11 together by a locking band 15 engaging the two sections, the band absorbs the drawing thrust and there is avoided the necessity for a heavy frame to Withstand the high forces developed in the drawing operation. As an example, a band weighing approximately 5000 pounds is capable of locking the sections against forces which would require a frame weighing approximately 500,000 pounds. A great saving of weight and cost is thus eifected.

In the absence of any further provision, the apparatus described above, with the exception of locking band 15, would function in a manner similar to devices heretofore employed, i. e., the punch 22 would have to overcome a force equal to the pressure per unit area in cavity 14 in section 10 multiplied by the area of the punch head. As stated in the introduction hereto, this would necessitate the application of large external forces on the punch in order to effect the forming operation. By this invention such forces are greatly reduced.

One of the principles employed in this invention consists in counteracting par-t or all of the pressure on the head of the punch by pressure on the rear of the punch, or, inflthe case of a movable pressure plate, to counteract all, or a part, of the pressure on one face of the plate by pressure on the opposite face. For this purpose the cavity 24 of easing section 1 1 is filled with a flexible member 101 of a substance acting like a. fluid under pressure, in

3 the same manner as cavity 14. The flexible material may be nlbber and may be provided with an annular expansible chamber 40 adapted to be filled with fluid under pressure, so that the pressure per unit area within cavity 24 may be brought up to a pressure on the order of the pressure which exists in cavity 14. For this purpose, the chamber 40 may be connected through conduit 41 and inlet 42 to the same source of pressure 32 as the annular chamber 30. In order to counteract the pressure on the head of the punch 22, the punch is provided on its opposite side With a reduced rear portion 43 so that the area at its opposite end is indicated by the distance AB. The pressure within cavity 24 will thus operate on the portion of the pun-ch indicated by the area CD minus the area AB. Therefore, over this area the pressure in 'cavity 24 will counteract the pressure on a similar area of the head of the punch applied thereto by the pressure in cavity 14. The only working forces which need therefore be applied to the punch to overcome the resisting force of the rubber are the pressure per unit area in cavity 14 multiplied by the area AB of the punch, and the frictional force acting on the cylindrical surface of the punch. It will be seen, therefore, that a very substantial portion 'of the resisting pressure in cavity 14 is counteracted by the pressure on the rear surface of the punch area CD minus AB. It will therefore require a greatly reduced external or working force to operate the punch.

Although the radial pressures acting upon the cylindrical surface 22 of the punch and the resulting force are considerable, the only portion of this force which resists the upward movement of the punch is the frictional force exerted against it. This force is rather limited since the frictional coefiicient is small. Thus where grease is used as a lubricant this coeflicient is .054.

The punch is connected to a ram 50 which is moved by hydraulic pressure entering from supply 45 by 'way of slots 46 in a bushing 47 into a chamber 48 where it acts upon a piston 49. The movement of the ram into the cavity 14 causes fluid to be displaced from chamber 51 through passage 52 and returned to the tank. These are usual and well known components of a forming apparatus of this type.

As the punch moves into cavity 14 "to the limiting posi- 'tion shown in dot-and-dash lines in Fig. 1, it reduces the volume within the cavity available to the rubber which fills it, and since the rubber is substantially incompressible, it would be necessary to relieve the rapid increase in pressure which would otherwise occur. This is effected by forcing fluid out of the annular chamber 30 to reduce the volume in the chamber. At the same time, the movement of the punch out of cavity 24 and into cavity 14 increases the volume available to the rubber in cavity 24 and would tend to decrease the pressure within the cavity. Such decrease is prevented by causing chamber 40 to expand. By interconnecting chambers 30 and 40 through conduits 33 and 41, the expansion of one chamber will permit corresponding contraction 'of the other chamber, thus tending to maintain the same volume relationship within cavities '14 and 24 regardless of the position of the punch, except for the volume of the punch ram. Since cavity 14 gains in the volume of punch 22 that enters therein, while cavity 24 loses a similar volume, these would ordinarily balance each other were it not for the fact that as the punch enters cavity 14, the ram 50 enters cavity 24 and would tend to increase the pressure in cavity 24. For this purpose, a suitable pressure control valve 32 is provided. The pressure can be controlled automatically to any desired value at any position of the punch.

In the form of the invention described in Fig. 1, it has been shown that the counteracting pressure has been applied to the rear-end of the punch in the area CD minus AB. This means that in order to overcome the resistance of the rubber in the female section when moving the punch, only enough force must be applied externally to the die equal to the pressure per unit area in cavity 14 multiplied by the area AB. However, if desired, counteracting pressure may be applied to the rear of the punch over an area equal to the area of the punch head, in which case the only external or working force necessary to operate the punch in the drawing movement will be the resistance of the metal to be formed and the frictional losses. For this purpose, as shown in Fig. .2, the ram may be provided with a frame 55 which extends above the casing portion 10 and is provided with a plunger extending slideably through said casing portion 10 into cavity 14. The area of plunger 56 is substantially the same as the area of ram 50, and the pressure in cavity 14 is substantially the same as the pressure in cavity 24. The force on the rear of the punch will therefore be increased by the unit pressure in cavity 14 multiplied by the area of plunger 56, so that the total force acting upwardly on the punch (the product of the pressure in chamber 14 and the area of ram 56, plus the product of the pressure in chamber 24 and area CD minus AB) will equal the total force acting downwardly (product of the area CD and the pressure in cavity 14). Thus the force on the head of the punch is equal to the force on the rear of the punch, whereby substantially no force other than that necessary to overcome the resistance of the metal and frictional losses need be applied to the punch.

In the Fig. 2 form there is also illustrated another method for obtaining the desired pressures in cavities 14 and 24 and for equalizing the volumes in the two cavities as the punch moves into cavity 14. For this purpose there is provided a pressure cylinder 60 supplied with pressure from any suitable source to force out .a piston rod 61 to which is pivoted at 62 a bell crank 63. The linear movement of piston rod 61 will move two plungers 64 and 65 in engagement with the bell crank arms into cavities 14 and 24 respectively, to compress the flexible members 102, 103 of rubber within said cavities and build up the pressures. As the punch 22 moves into cavity 14 to tend to decrease the volume therein, the plunger 64 is moved out of the cavity to rock bell crank 63 around its pivot 62 and force plunger 65 into cavity 24, to tend to decrease the volume in cavity '24, thus serving to maintain the pressure equilibrium on the two sides of the punch.

In this form 'of the invention the casing sections 10 and 11 are provided with cooperating flanges 10 and 11 which may be locked by C-type clamps 15.

In Fig. 3 there is disclosed another form of the invention in which the pressure on the punch head is completely counteracted by the pressure on the rear of the punch. In this form of the invention in addition to causing counteracting pressure to act on that portion of the piston rear surface denoted by area CD minus area AB, counteracting pressure is also applied to the area AB. For this purpose the end 66 of ram 50 operates within a cavity 67 which is in communication with the cavity 24. The transfer of pressures between the flexible member 104 in cavity 14 on the one hand and the flexible means 105 in cavities 24 and 67 on the other hand may be effected in the manner shown in Fig. l or in the manner shown in Fig. 2, or by still another method, as disclosed in Fig. 3. By the Fig. 3 method the pressure plate 20 is provided with a plurality of perforations 70 through which the flexible member 104 may flow between cavity 14 and cavity 24 as the punch 22 moves into cavity 14 and out of cavity 24. As shown in Fig. 3, a hydraulic cylinder is arranged within cavity 24 to operate punch 22.

Still another advantage of the process and apparatus hereinbefore described is illustrated in Figs. 4A and 4B. This advantage arises in cases where the punch does not initially occupy the entire space within the pressure plate opening, as in the case where the shape of the finished article when drawn is a cone. In such instances it Will readily be apparent that with the method heretofore employed wherein only the upper chamber above the blank was under pressure, there was an initial period during the movement of the punch in which the metal of the blank was unsupported because of the gap 79 which necessarily existed between the reduced end 80 of the punch and the opening 21 in the pressure plate. The metal tended to be forced through this gap as shown at 81 because the blank had to sustain the full rubber pressure which is required to clamp the edges of the blank against wrinkling. In those cases where the unsupported gap was large it sometimes resulted in rupture of the blank in the early stages of the draw stroke. However by the method described herein in which the same order of unit pressures exist above and below the blank, the under surface of the blank in the region of the unsupported area is supported during the clamping and initial stages of the draw stroke as shown in Fig. 4B, thus making it possible to start the drawing of such pieces successfully without danger of rupture of the blank.

In Fig. 5 there is disclosed still another method for maintaining the relative pressures in cavities 14 and 24 constant in spite of the entry of punch 22 into the female die section and the corresponding movement of the punch out of the male die section. In this form of the invention the entry of punch 22 into cavity 14, with the consequent tendency to increase pressure, is compensated for by the movement of the pressure plate 20 in an opposite direction relative to the punch, so that as punch 22 moves toward the female die section, the displaced flexible member 106 in said section causes plate 20 to move toward the male section to take up the loss of volume caused by the movement of the punch out of cavity 24. Here it will be noted that the pressure plate 20 is not supported adjacent its periphery between casing sections and 11, as in the Figs. 1 to 3 forms, but has its entire area unsupported by the casing. The pressure plate floats between the flexible members 106, 107, being substantially balanced by the pressure above and below it.

In the forms of the invention disclosed in Figs. 1, 2, and 3, the relative movement between the pressure plate and the punch was accomplished by fixing the pressure plate and moving the punch. In the Fig. 5 form of the invention the relative movement between pressure plate and punch was accomplished by making both the plate and the punch movable in opposite directions. Still an other method of accomplishing relative movement bebetween pressure plate and punch may be obtained by the method disclosed in Fig. 6 in which the punch 22 is fixed to the casing section 11 and only the pressure plate is movable. In this form of the invention the entire forming force must be developed by the movement of the pressure plate, and for this purpose the plate may be supported on piston rods 85 fixed to pistons 86 operating within cylinders 87 which may be provided with the inlet and outlet passages 88 and 89 through which fluid under pressure may be introduced and discharged through suitable connections 90 and 91. Thus when it is desired to form a blank, pressure is supplied through passages 88 in cylinders 87 and metered out through passages 89 by valve 92, moving the pistons and pressure plate 20 downwardly. This creates excess pressure in the flexible member 109 in cavity 24 but such pressure is transferred to the flexible member 108 in cavity 14 by the sets of annular chambers 30 and 40 and their connections 33 as shown in Fig. 1. The pressure thus transmitted to cavity 14 forces the blank down over the head of punch 22 which is gradually exposed as the pressure plate moves downwardly. It will be seen that the necessary external force acting on rods 85 is but a small fraction of that which would have been required if the pressure in the flexible members 108, 109 were not equalized in the manner described. As a consequence, relatively little external force is required to move the pressure plate.

Having described my invention, what I claim and desire to secure by Letters Patent is:

1. An apparatus for forming a metal blank, comprising a casing composed of aflrst section and a second section, a blank supporting means positioned between said sections and having an opening therein, means for locking said sections together, a punch normally positioned in said first section and adapted to operate in said opening of the blank supporting means, said punch having a head and a reduced rear portion, a flexible member in the first section in direct engagement with the head and reduced rear portion of the punch and with the blank supporting means, a flexible member in the second section in direct engagement with the blank, both flexible members acting like a fluid under pressure, actuating means for effecting relative movement between the punch and the blank supporting means, and means for equalizing the pressures in both flexible members at any position of the punch.

2. An apparatus as specified in claim 1, in which the means for locking the casing sections together comprise a band rotatably supported on one of said sections and having a bayonet lock engagement with the other section.

3. An apparatus as specified in claim 1, in which the equalizing means comprise an expansible chamber in each flexible member, said chambers being filled with a fluid under pressure, and a fluid conduit connecting said chambers.

4. An apparatus as specified in claim 1, in which the equalizing means comprise a plunger in each section, said plungers being movable independently of said punch and subject to pressure exerted by the flexible members in said sections, and mechanism interconnecting said plungers so that when one plunger is forced to rccede from its section, the other plunger will be caused to advance into the other section.

5. An apparatus as specified in claim 1, in which the equalizing means comprise perforations in the blank supporting means, said perforations being spaced from said punch receiving opening, whereby a portion of the flexible member of the second section may flow into the first section when the punch is received in said second section.

6. An apparatus as specified in claim 1, in which the blank supporting means floats between said flexible members.

7. An apparatus for forming a metal blank, comprising a casing composed of a first section and a second section, means for locking said sections together, a pressure plate supported by said casing between said sections and adapted to support the blank to be formed, said plate having an area unsupported by said casing and having an opening therethrough, a punch normally positioned in the first section and adapted to operate in the opening, said punch having a head and a reduced rear position, a flexible member in the first section in direct engagement with the head and reduced rear portion of the punch and with the plate, a flexible member in the second section in direct engagement with the blank, both flexible members acting like a fluid under pressure, actuating means for effecting relative movement between the punch and the pressure plate, and means for equalizing the pressures in both flexible members at any position of the punch.

References Cited in the file of this patent UNITED STATES PATENTS 1,177,240 Gales Mar. 28, 1916 1,930,745 Fisher Oct. 17, 1933 2,075,847 Hothersal Apr. 6, 1937 2,111,695 Seeber et al Mar. 22, 1938 2,317,869 Walton Apr. 27, 1943 2,375,599 Walton May 8, 1945 2,422,883 Bruderlin June 24, 1947 2,507,194 Chyba May 9, 1950 2,519,661 Johnson Aug. 22, 1950 2,565,949 Clifford et al Aug. 28, 1951 

1. AN APPARATUS FOR FORMING A METAL BLANK, COMPRISING A CASING COMPOSED TO A FIRST SECTION AND A SECOND SECTION, A BLANK SUPPORTING MEANS POSITIONED BETWEEN SAID SECTIONS AND HAVING AN OPENING THEREIN, MEANS FOR LOCKING SAID SECTIONS TOGETHER, A PUNCH NORMALLY POSITIONED IN SAID FIRST SECTION AND ADAPTED TO OPERATE IN SAID OPENING OF THE BLANK SUPPORTING MEANS, SAID PUNCH HAVING A HEAD AND A REDUCED REAR PORTION, A FLEXIBLE MEMBER IN THE FIRST SECTION IN DIRECT ENGAGEMENT WITH THE HEAD AND REDUCED REAR PORTION OF THE PUNCH AND WITH THE BLANK SUPPORTING MEANS, A FLEXIBLE MEMBER IN THE SECOND SECTION IN DIRECT ENGAGEMENT WITH THE BLANK, BOTH FLEXIBLE MEMBERS ACTING LIKE A FLUID UNDER PRESSURE, ACTUATING MEANS FOR EFFECTING RELATIVE MOVEMENT BETWEEN THE PUNCH AND THE BLANK SUP- 